1. Field of the Invention
The present invention is related generally to the field of internal combustion engine exhaust gas recirculation (EGR) for emissions improvement. More particularly, the invention provides a turbocharger compressor wheel having impeller vanes mounted on a side opposite the compressor impeller to act as an EGR pump with a separate diffuser and volute for EGR flow output from the pump and a separate scroll inlet to the EGR pump; a control valve for metering exhaust gas to be recirculated and a mixer for entraining the recirculated exhaust gas in the charge air for the engine.
2. Description of the Related Art
EGR is a known method for reducing the NOX emissions in internal combustion engines. For effective use, an EGR system must overcome the adverse pressure gradient created by a positive pressure gradient across the engine which is typical of modern high efficiency diesel engines in at least a portion of their operating range. Various approaches to implementing EGR have included pumping of a portion of the exhaust gas from the exhaust manifold to the intake manifold. Pumping has been accomplished by introducing the exhaust gas into the compression inlet of a conventional turbocharger or supercharger present on the engine or, alternatively, providing a separate compressor receiving the exhaust gas and pressurizing it to a suitable pressure for insertion into the charge air downstream of the charge air boosting system on the engine. Some fuel consumption penalty is generally incurred by these systems.
EGR also requires adequate mixing of recirculated exhaust gas with the incoming fresh air charge to avoid performance degradation and to minimize mixing losses to avoid additional fuel consumption penalties. Further, positive control of the recirculated exhaust gas flow is required to assure proper proportions in the charge air mixture supplied to the engine intake manifold under varying operating conditions. Additionally, the components and features of an EGR system must be accommodated within the constraints of limited volume available for allocation in modern engine compartments.
It is, therefore, desirable to provide a highly integrated EGR system employing pumping components for recirculation of exhaust gas in close physical and functional cooperation with existing engine system components such as turbochargers. It is further desirable to configure an EGR flow path and provide novel control components to allow necessary control over exhaust gas flow rates and mixing into the charge air for aspiration by the engine to minimize variation of the percentage of exhaust gas from cylinder to cylinder.